Autocar: Tesla Model S vs Aston Martin Rapide S

[anonymous-user]

98elise said:

Max_Torque said:

I sorry, but that ridiculous touch screen, which looks to have been specifically developed for people with poor eyesight, is THE most distracting thing i have ever seen in a car since Keira Knightley stopped doing a spot of taxicabing on the weekends.



And, electric cars aren't going to be properly fast until they get more than 1 gear..........

Why do you need more than one gear? Gears are used to overcome the issue that ICE engines have with rev/torque limitations. EV's don't really need gears or a clutch.

Because flyheel (or Emotor) torque is irrelevant. What matters is Wheel Torque, which is equivalent to the Power produced by your powertrain, not the torque! So, yes an electric machine can make good torque at low speeds, but it doesn't make good power at low speeds. Now there are some 'tricks' you can do (like employing field weakening strategies) to broaden the constant power region of your Emachine, but they can't get you to peak power rpm with a single fixed gear ratio until the vehicle speed is high enough.

[williamp]

98elise said:

moreflaps said:

williamp said:

a remarkable car indeed. All that space and power, and similar performance to the Rapide, with a similar range. Yet the cost to refill is just £4. And at 6 hours, something which can be achieved at work or overnight.

If work lets you suck the kW of course...

My place of work has free charging points at every office

...and if you can afford a tesla S, the chances are you arevun a position of influence within the company.

If anythign else, it is the first sign that elecric power could be a geniune competition for the internal combusion engine. Keep the petrol for le mans, for most of us, most of the range would be fine

[sofaking]

Vipers said:

Thought it was a lot less than that. Managed to sit in one in a showroom last month in Bellevue, fantastic interior, dash board better than Star Trek, just looked so alien having no "Engine", just an electric motor on each back axel.

The interior on the few for sale used that I saw look really naff. Aside from the huge screen, the plastics and seating look decidedly low rent. This is all from online ads though. Your comments have me interested in going for a look at one in person now.

[Vipers]

Max_Torque said:

And, electric cars aren't going to be properly fast until they get more than 1 gear..........

With our roads, why worry.

[vladcjelli]

Max_Torque said:

And, electric cars aren't going to be properly fast until they get more than 1 gear..........

I think I've asked this question before, but can't remember the answer. Seeing you, an expert of some sort, ask it suggests there has been no useful answer yet.

You mention the performance benefits, but surely there must be an efficiency benefit too?

If an electric motor requires x amount of power to run at y (45mph), then travelling at z (nsl) would return less mpw (miles per watt?).

So as with ICE, less rpm results in less power consumed?

[Otispunkmeyer]

he said iPad like screen in the dash

WTF that thing looks huge, like having a 20 inch monitor in your dash board. Is Xzibit on the design team?

still, great piece of engineering. 265 mi genuine range and ability to charge in a reasonable amount of time and about £4 to fill up! what is not to like? (apart from the fact that if we keep trying foist wind turbines on everyone, no one will be able to run such a car).

[Otispunkmeyer]

vladcjelli said:

Max_Torque said:

And, electric cars aren't going to be properly fast until they get more than 1 gear..........

I think I've asked this question before, but can't remember the answer. Seeing you, an expert of some sort, ask it suggests there has been no useful answer yet.

You mention the performance benefits, but surely there must be an efficiency benefit too?

If an electric motor requires x amount of power to run at y (45mph), then travelling at z (nsl) would return less mpw (miles per watt?).

So as with ICE, less rpm results in less power consumed?

I think as well NVH comes into it. Without an ICE clattering away under the hood you'd be surprised at what other noises are going on. Gears "whine" when they're meshing at high speed. You don't want that on a car that is practically silent from the inside and you dont want to be spending lots of dosh on sound proofing.

Having said that, there must be a final drive or at least one gear in these things, I don;t think they'd bolt the drive shaft directly out to the wheels? or do they?

[DoctorX]

I wonder how much of the purchase price constitutes the luxury car and how much represents the drivetrain? Surely if they wrapped something a bit more run of the mill around the electric bits and sell for less they'd sell a stload of these...

[AER]

Max_Torque said:

I sorry, but that ridiculous touch screen, which looks to have been specifically developed for people with poor eyesight, is THE most distracting thing i have ever seen in a car since Keira Knightley stopped doing a spot of taxicabing on the weekends.



And, electric cars aren't going to be properly fast until they get more than 1 gear..........

I agree. That screen is the most jarring thing of the whole package. They should have perhaps split the thing into two screens or at least attempted to integrate the screen into the shape of the interior better. As it is now, it screams afterthought.

[anonymous-user]

vladcjelli said:

Max_Torque said:

And, electric cars aren't going to be properly fast until they get more than 1 gear..........

I think I've asked this question before, but can't remember the answer. Seeing you, an expert of some sort, ask it suggests there has been no useful answer yet.

You mention the performance benefits, but surely there must be an efficiency benefit too?

If an electric motor requires x amount of power to run at y (45mph), then travelling at z (nsl) would return less mpw (miles per watt?).

So as with ICE, less rpm results in less power consumed?

A modern brushless synchrounous motor, driven by a varriable frequency inverter is a very flexible device, but it, like the IC engines before it, still has a number of design compromises that must be addressed at fundamental design stage. Because of the cost and complexity of these hybrid cars, to date, most vehicles have simple opted for a single fixed gear ratio drive.

This give two main design points.
1) maximum tractive effort at zero rpm (Emotor torque at zero speed x gear ratio / tyre radius)
2) maximum vehicle speed (Emotor max rpm limit)

The max tractive effort one is particularly difficult, because with a loaded car, even driving over say a kerb takes a huge amount of force, let alone trying to get a fully loaded car up a steep US style drive etc

Using field weakening techniques, the motors constant power operating region can be extended, generally to something like 2x the non field weakened rpm range. (although, in reality, iron losses & inverter max frequency (& the motor winding coils max voltage rating due to fast dv/dt switching required) limit the efficiency, and hence the power, during extreme field weakening).

So, you want the most tractive effort you can get, and the lowest motor torque to deliver that (because in effect, it is the torque that 'costs' you terms of motor size, the amount of copper/iron, the size of the power silicon in your inverter etc) But, that then forces you to use a numerically high ratio between the motor and the wheels, which then means either you need a high speed motor (expensive, needing things like a carbon fibre reinforced and internal oil/water cooled rotor etc) or you have to limit the max speed of the vehicle.

To date, most EV's have chosen to limit the Vmax (because they have generally not been 'sports' variants, and a lack gradability could be a serious customer concern). However, the latest sports hybrids are going to find this lack of gears becoming seriously limiting and in fact, cars like bmw i8 do have a multispeed gearbox attached to the motor.

In terms of efficiency, pure Emotor rotational velocity is not as critical as for an ICE. There are not the NVH concerns, and internal friction is pretty much entirely rotational, so the pure mechanical friction characteristic with speed is very low. However, depending on the architecture, iron losses and the resultant internal rotor heating do start to become a significant issue as the motor approaches peak power rpm (in field weakening, copper losses also start to dominate because a huge proportion of the magnetic flux (and hence winding current) is being used to suppress the backEMF, rather than act to produce torque)
So, downspeeding the emachine is a good thing to do and brings a small but welcome efficiency advantage.

[Devil2575]

Max_Torque said:

And, electric cars aren't going to be properly fast until they get more than 1 gear..........

Properly fast? So you don't regard 0-60 in 4.6 seconds as quick?

I can understand why this car is selling so well. A fraction of the fuel costs of the equivalent conventionally powered car, decent range, reasonable recharge time and well priced.

Lots of people dismissed electric cars a couple of years ago, how wrong they were.

Edited by Devil2575 on Sunday 8th September 11:58

[anonymous-user]

Devil2575 said:

Max_Torque said:

And, electric cars aren't going to be properly fast until they get more than 1 gear..........

Properly fast? So you don't regard 0-60 in 4.6 seconds as quick?

The model s has a top speed of 130mph, so chances are the Emachine peak power is reached just slight above half of that (say ~80mph) (allowing a little under 2x the normal speed range in field weakening mode). As such, until the car reached 80mph, it is not producing peak power. As the power curve for an emachine is broadly speaking linear (assuming constant torque (it will be inverter power silicon limited in the short term), even a two speed gearbox would result in 25% more available tractive effort, and possibly a sub 4sec 0-60!

[Vipers]

Does 2 seconds 0 to 60 make any difference on our roads, and where would this make any difference on the roads, I am all ears.

[E38Ross]

Vipers said:

Does 2 seconds 0 to 60 make any difference on our roads, and where would this make any difference on the roads, I am all ears.

Of course it makes a difference. My old mans current car is 4.8 to 60. His last car was 6.7.

I can tell you that when it comes to overtaking you can do much more with the current car, with a lot more confidence than his last car. It also means it gives more G under acceleration which in itself is quite a thrill. A car quicker 0-60 is often quicker from and to other speeds as well you know.... Where it matters more on the road.

[Devil2575]

Max_Torque said:

The model s has a top speed of 130mph, so chances are the Emachine peak power is reached just slight above half of that (say ~80mph) (allowing a little under 2x the normal speed range in field weakening mode). As such, until the car reached 80mph, it is not producing peak power. As the power curve for an emachine is broadly speaking linear (assuming constant torque (it will be inverter power silicon limited in the short term), even a two speed gearbox would result in 25% more available tractive effort, and possibly a sub 4sec 0-60!

But why bother?

130 mph is fast enough as is it's accelleration figures?

It's not a sports car after all.

[Chicane-UK]

Viper_Larry said:

They are everywhere here in California and look great! Really stylish on the road - my current favourite.

Totally! Was out in San Francisco the week before last and I hoped to see one on the road.. Think I saw about 10 in the end. Clearly they have been a massive success there. Can't wait for them to get a bit more ubiquitous as I really want to drive one! Look fantastic too :-)

[AnotherClarkey]

Max_Torque said:

Devil2575 said:

Max_Torque said:

And, electric cars aren't going to be properly fast until they get more than 1 gear..........

Properly fast? So you don't regard 0-60 in 4.6 seconds as quick?

The model s has a top speed of 130mph, so chances are the Emachine peak power is reached just slight above half of that (say ~80mph) (allowing a little under 2x the normal speed range in field weakening mode). As such, until the car reached 80mph, it is not producing peak power. As the power curve for an emachine is broadly speaking linear (assuming constant torque (it will be inverter power silicon limited in the short term), even a two speed gearbox would result in 25% more available tractive effort, and possibly a sub 4sec 0-60!

ISTRC that the original plan for the Tesla Roadster was to have a 2 speed box but they never got it quite right for production?

[kambites]

AnotherClarkey said:

ISTRC that the orginal plan for the Tesla Roadster was to have a 2 speed box but they never got it quite right for production?

I seem to remember that first gear kept disintegrating.

[AnotherClarkey]

kambites said:

AnotherClarkey said:

ISTRC that the orginal plan for the Tesla Roadster was to have a 2 speed box but they never got it quite right for production?

I seem to remember that first gear kept disintegrating.

Yes, I would rather have no gearbox than one which craps out.

[anonymous-user]

Devil2575 said:

Max_Torque said:

The model s has a top speed of 130mph, so chances are the Emachine peak power is reached just slight above half of that (say ~80mph) (allowing a little under 2x the normal speed range in field weakening mode). As such, until the car reached 80mph, it is not producing peak power. As the power curve for an emachine is broadly speaking linear (assuming constant torque (it will be inverter power silicon limited in the short term), even a two speed gearbox would result in 25% more available tractive effort, and possibly a sub 4sec 0-60!

But why bother?

130 mph is fast enough as is it's accelleration figures?

It's not a sports car after all.

Ok, keep the current performance, and knock off 25% of the cost of your battery, inverter and motorsystems then..........